Intraoperative Cyclorotation and Pupil Centroid Shift During LASIK and PRK

Abstract

Significant changes in cyclotorsion and centroid shifts were noted prior to surgery as well as intraoperatively with both LASIK and PRK. It may be advantageous to engage iris registration immediately prior to ablation to provide a reference point representative of eye position at the initiation of laser delivery.

Effect of Iris registration on visual outcome in wavefront-guided LASEK for myopic astigmatism

“…Similarly, Moshirfar et al [2] also reported an IR success rate of 65%, which was well within the ranges of 50% [7] to 93% according to other studies [2]. Failure of iris capture occurs in eyes with large rotational angles or pupil movement greater than 0.5 mm [18]. In this study, the measurement of cyclotorsion was available only for the IR group; the rotational angle could not be confirmed in the Failed-IR group.…”

“…a In the IR group, log contrast sensitivity of 12 cpd (P = 0.001) and 18 cpd (P = 0.019) increased. b In the Non-IR group, contrast sensitivity values of 6 cpd (P \ 0.001) and 12 cpd (P = 0.001) increased (Wilcoxon signed-rank test) enlargement of the pupil diameter to more than 7 mm and pupil \3.0 mm are known to cause the failure of IR [2,18]. The authors tried to show the association of IR failure and pupil size.…”

“…IR is aimed at reducing the alignment errors between wavefront measurements and the subsequent ablation [18]. A 4-degree misalignment would result in a 14% Fig.…”

“…Our finding that IR failed to show superior outcomes in astigmatism correction potentially resulted from the recorded 2.1°o f cyclotorsion evident in the IR group. It was suggested that under well-controlled surgical conditions, no difference exists in the outcomes between the IR and Non-IR system [18].…”

“…According to Febbraro et al [25], the rotational eye movements are mainly static preoperatively, but have a significant amplitude during photo-ablation with a mean 2.69°of cyclotorsion (range 0.0°-9.2°). Thus, better outcomes could be achieved using IR with a dynamic rotational eye tracker in the astigmatism correction, especially in cases of eyes with intraoperative cyclotorsion[2° [18].…”